The Aprilaire 4655 Humidistat is designed for low voltage service to control humidification equipment. An increase in relative humidity expands the nylon ribbon which opens the control switch to stop operation of the humidifier. A decrease in relative humidity reverses the process and closes the control switch. Can be wall mounted or mounted on return plenum. Includes plenum cutout template (4 5/32" X 2 7/16"). For duct mount, locate at least 6" upstream of humidifier, humidifier bypass ductwork or fresh air intake ductwork.

I didn't exactly follow the instructions when installing on the intake ductof the furnace. The old nonworking humidistat required a smaller opening. I didn't use the supplied template to cut a larger opening. I duct taped the opening shut and then used only two screws (in the top) to mount the 4655 humidistat onto the outside of the intake duct. The bottom of the 4655 humidistat angels out at the bottom allowing air flow.

I have only had it installed a couple of weeks, but so far, so good. Back to a very comfortable house in a cold, dry climate. I knew it would be smaller than the original and the hole in the return would be too large. I just removed the humidistat from the frame and put it in the old frame. In warm weather, I can do the sheet metal repair so that the new frame will fit perfectly.

My original humidistat failed and purchased this as a replacement. I received this in a matter of days and took about 5 minutes to install. This was the same unit that was recommended by my hvac company I use for service. It cost less than half the price I was going yo pay locally. I will definitely buy from here in the future! I would recommend to anyone

We bought this to replace an old gold humidistat that was probably from the 80s or earlier. The knob on the old unit was broken off and couldn't be repaired. The new unit is slightly bigger but we made it fit. It took us a long time to figure out that the two posts for wires simply made a circuit and there wasn't a positive or negative. Either that or we got lucky with the first combination we tired. At any rate, once we finished deliberating about positive and negative posts, it took about 10 minutes to install it. It probably would go faster if someone with ANY amount of experience was doing it. But, we managed to get it on and running and not electrocute ourselves, so it's a win!

I didn't exactly follow the instructions when installing on the intake ductof the furnace. The old nonworking humidistat required a smaller opening. I didn't use the supplied template to cut a larger opening. I duct taped the opening shut and then used only two screws (in the top) to mount the 4655 humidistat onto the outside of the intake duct. The bottom of the 4655 humidistat angels out at the bottom allowing air flow.

I have only had it installed a couple of weeks, but so far, so good. Back to a very comfortable house in a cold, dry climate. I knew it would be smaller than the original and the hole in the return would be too large. I just removed the humidistat from the frame and put it in the old frame. In warm weather, I can do the sheet metal repair so that the new frame will fit perfectly.

My original humidistat failed and purchased this as a replacement. I received this in a matter of days and took about 5 minutes to install. This was the same unit that was recommended by my hvac company I use for service. It cost less than half the price I was going yo pay locally. I will definitely buy from here in the future! I would recommend to anyone

We bought this to replace an old gold humidistat that was probably from the 80s or earlier. The knob on the old unit was broken off and couldn't be repaired. The new unit is slightly bigger but we made it fit. It took us a long time to figure out that the two posts for wires simply made a circuit and there wasn't a positive or negative. Either that or we got lucky with the first combination we tired. At any rate, once we finished deliberating about positive and negative posts, it took about 10 minutes to install it. It probably would go faster if someone with ANY amount of experience was doing it. But, we managed to get it on and running and not electrocute ourselves, so it's a win!

The Aprilaire 4655 Humidistat is designed for low voltage service to control humidification equipment. An increase in relative humidity expands the nylon ribbon which opens the control switch to stop operation of the humidifier. A decrease in relative humidity reverses the process and closes the control switch. Can be wall mounted or mounted on return plenum. Includes plenum cutout template (4 5/32" X 2 7/16"). For duct mount, locate at least 6" upstream of humidifier, humidifier bypass ductwork or fresh air intake ductwork.